2007-02-15
Telia Free 20 wireless phone
This phone was brand new and it worked fine when we got it. The
battery died very quickly, though. It really should have gone
back to the shop as a warranty repair. The problem was that
there was really no shop since it came as a "gift" by mail
because we changed phone company and it would have had to be
sent back. So I decided to take a look at it. It tuned out that
there was no indication on the phone when it was put into the
base module (the charger), there is normally a beep or
something. I also manually charged the batteries since it was
three standard AAA cells. It then worked fine again for a while
and then died, typically during a conversation. This means that
it had to be the charging circuit. I first checked the base
module and it seemed fine. There was a reasonable voltage and
current for charging. I then dismantled the phone which was
quite easy, it can be rather tricky without the proper tools and
knowing exactly how to do it. I started to do some measurements
and everything seemed fine, except it wasn't charging. Since I
didn't have a schematic for it I tried to draw one myself which
was a bit hard because of SMD components with cryptic branding.
After some digging on the internet I found out what the
components where and could do a schematics for the charging
circuit. On the circuit board there where a lot of components
missing, probably for features not present in this model. There
was one resistor missing which, if it where there would make the
circuit work. So I put in one resistor of a value that seemed
OK, it wasn't a critical value for the circuit. Unfortunately I
didn't have the right size so I had to put in a 0805 resistor in
where there should be a 0406. After that it worked just fine.
2007-02-15
Telia Free 20 wireless phone